1. Field of the Invention
The present invention broadly relates to a device for changing the current flow through a ferrimagnetic load so as to affect the magnetic flux imparted to the load, and deals more particularly with a device-implemented method for driving a phase shifter for an antenna array in which the magnetic flux imparted to the phase shifter is precisely metered.
2. Description of Related Art
Phase shifters are used as primary components in electronically controlled array antennas. An array antenna contains many individual radiating elements. By properly controlling the phase of each element, the resulting beam of the antenna can be steered electronically. By using a so-called reciprocal phase shifter, the same antenna can be used as a receiving antenna with a steerable beam.
Ferrite phase shifters employed in array antennas are formed by placing ferrite materials in a section of a waveguide. The ferrite phase shifter can be either a reciprocal or non-reciprocal device depending upon its configuration. In a reciprocal phase shifter, phase shifting is accomplished by changing the magnetic permeability of the ferrite through changing the externally applied DC magnetic field. Non-reciprocal ferrite phase shifters provide a shift in microwave phase dependent upon the amount of remanent magnetism in the ferromagnetic element. A coil of wire, forming an inductive load, is normally used to alter the strength of the magnetic field in a reciprocal phase shifter. The strength of the field in a non-reciprocal phase shifter is a function of voltage across its toroidal winding versus the period of time that the voltage is applied.
In the past, the strength of the magnetic field was controlled by controlling the time period for which the voltage was applied to the coil. In order to accomplish this, the switching speeds of the control element were required to be extremely fast and it was also necessary that the applied voltage be controlled very precisely. U.S. Pat. Nos. 3,947,776 and 4,469,961, respectively issued Mar. 30, 1976 and Sept. 4, 1984, exemplify prior approaches for driving inductive loads, such as phase shifters, which rely on extremely fast switching times. Specifically, the arrangements in these prior patents relate to reciprocal-type phase shifters for establishing and then sustaining a current flow by reducing the drive voltage. These previous systems were less than completely satisfactory in terms of their speed and accuracy because of variables which affect the switching time, such as variations in rise time, voltage drops on the power supply and temperature variations.
The present invention is directed toward overcoming the above-mentioned deficiencies.